Apparatus for burning solid fuels



July 23, 1957 D. M. MCLAREN 2,800,094

APPARATUS FOR BURNING 501.10 FUELS 1 Filed Feb. 25, 1955 2 Sheets-Shee t 1 i I Tlql.

I INVENTOR 1 130M010 M. Mc'lnmsw ATTORNEY D. M. MOLAREN 2,800,094

APPARATUS FOR BURNING SOLID FUELS July 23, 1957 2 Sheets-Sheet 2 Filed Feb. 25. 1953 INVENTOR po/wuonuczpfiav ATTORNEY United States PatentO APPARATUS FOR BURNING SOLID FUELS Donald M. McLaren, Glasgow, Scotland, assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application February 25, 1953, Serial No. 338,754

Claims priority, application Great Britain February 27, 1952 2 Claims. (Cl. 110-1055) The present invention relates to apparatus for the combustion of solid fuels, and more particularly to the construction and operation of spreader stokers wherein fuel is projected into the furnace by a jet or jets of elastic fluid.

In accordance with the invention granular solid fuel, such as crushed bituminous coal, is projected into a furnace by a jet of elastic fuel, with the initial acceleration of the fuel occurring in a generally horizontal direction followed by a downward direction to obtain a desirable distribution of the fuel transversely of the furnace. Advantageously, the elastic fluid may consist of air at relatively low pressure and volume, with the air used for mixing and accelerated combustion of the fuel within the furnace. The air jet causes segregation of the fuel sizes with the coarser particles distributed over the transverse area of the furnace. The fines are distributed so that a large portion thereof are directed downwardly by the downward movement of the air jet to be deposited on a grate downwardly adjacent the position of the spreader stoker. Some minor portion of the fines will be projected across the furnace and will burn in suspension. The invention is particularly effective in burning crushed solid fuels having a high percentage of fines, and avoiding carbon loss by reason of the presence of unburned fine fuel particles in the ash discharged from the furnace. A moving grate is positioned in the lower portion of the furnace to support the ash and unburned fuel delivered thereto by the spreader stoker. The fuel and ash supporting surface of the moving grate moves from the front wall of the furnace, beneath the spreader stoker, toward the opposite wall.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described preferred embodiments of my invention.

Of the drawings:

Fig. 1 is an elevation in longitudinal section through the lower portion of the front part of a spreader stoker fired furnace constructed and arranged in accordance with the invention;

Fig. 2 is a part of Fig. 1 to a larger scale, including a spreader unit;

Fig. 3 is a plan of part of the furnace coal supply mechanism, including two adjacent spreader units taken on the line 33 of Fig. 1; and

Figs. 4, 5 and 6 illustrate modifications of the feeder units shown in Figs. 1 to 3.

Referring to Figs. 1 to 3 of the drawings, the furnace has a front wall 1 bounding a combustion space 3 above a travelling grate 4 of the chain grate type arranged so that its upper run moves rearwardly.

In front of and extending laterally of the front wall 1 is arranged a hopper 5, into which coal is led from an overhead bunker 6 through a traversing chute 7. At the bottom of the hopper and arranged side by side in a row extending laterally of the furnace are a number of feeders 8 operating on the endless conveying surface principle. The feeders are arranged during operation to remove coal rearwardly from the hopper. Suitably all the feeders are driven at the same speed by common driving means. The amounts of coal fed by the feeders can be adjusted individually by raising or lowering guillotine doors 9 positioned above the rear end of the feeders and slidable within the rear wall 10, which is a double wall of the hopper.

Coal is prevented from falling in front of the feeders by plates 11 and from falling between the feeders by ridged structures 12.

' The coal from the rear ends of the feeders is arranged to fall onto a common chute 13 sloping downwardly and rearwardly. At the bottom of the chute behind each feeder is a plate 14 of a respective spreader unit 15, which is arranged to receive the coal falling from the rear end of the feeder. The chute is provided with structures 16 of refractory between adjacent spreader units, which are formed with sloping surfaces 17 normal to the main surface of the chute and adapted to direct the falling coal to paths leading them to the spreader units.

Adjacent each spreader unit plate 14 the lowermost part of the chute is formed by a metal block 19. The surface of chute above these blocks, between the refractory structures 16 and above the level thereof, is formed by the surfaces of refractory bricks 21).

A fixed scraper plate 21 is provided adjacent the rear of each feeder to insure the falling from the feeder conveying surface of coal that might otherwise adhere thereto. A screen 22 projecting downwardly and forwardly from the furnace front wall 1 near the bottom thereof is provided for intercepting radiation from the furnace that might damage mechanical parts of the feeders. In the illustrated embodiment of the invention, the

center lines of adjacent spreader units are 1 9 /2" apart.

Each spreader unit plate 14 is bolted to the block 19 and has a shelf 23 extending horizontally and rearwardly from the bottom of the chute a distance of 5"; the rear part of the plate is formed as a deflector which curves downwardly, the curvature being cylindrical around a laterally extending axis distant 6 from the upper surface of the plate; the plate terminates where the slope thereof has an angle of 45, or thereabouts, to the horizontal. The side edges of the plate diverge rearwardly, being 10% apart at the front of the shelf and 16 /2 apart at the rear edge of the deflector. The side edges of the plate are furnished with upstanding guide walls 26 having their upper edges horizontal and at a height of 2 /2 above the level of the shelf 23 and provided with forward and upward extensions 27 defining the path of the coal falling over the part of the chute provided by the block 19. The spreader unit is located so that the shelf 23 is 12%" above the grate.

The spreader stoker unit also comprises a horizontally directed elongated orifice 30 formed in the block 19. The orifice is 10" wide and deep with its lower edge /2" above the plane of the shelf 23. The orifice registers with a slot 31 in a duct 32 extending adjacent the lower ends of the chute transversely of the furnace and arranged to supply air to all the spreader units.

porting the refractory blocks 20 and having curved parts conforming to the shape of the duct 32.

As described in a copending application of William M. Urquhart, Serial No. 338,797, filed February 25, 1953, the chain grate 4 may be provided with air compartments beneath different zones thereof, and the furnace may be provided adjacent a rear arch at the lower end of its rear wall with a downwardly extending shield, a ledge, and an air orifice for reprojecting forwardly into the combustion space coal which may deposit on the ledge.

In operation, coal prepared for spreader stoker firing, e. g. crushed and capable of passing through a /2" ring, is fed from the bunker 6 through the traversing chute 7 to the hopper 5, and the feeders 8 are operated to discharge coal continuously from the hopper to the spreader units 15. Air is supplied to the duct 31 at a pressure of 12" to 18" water gauge, and after issuing from the orifices 30 continuously projects coal rearwardly from the spreader units. Less than percent of the total combustion air required for the fuel delivered to the furnace is required for the air jet action described. Under some conditions, as in serving a furnace having unusually great length, a somewhat greater proportion of air may be required. The coal particles or lumps so supplied to the furnace burn partly in suspension in the combustion space above the fuel bed and partly in the fuel bed on the grate 4.

The feeders 3 supply coal continuously to the spreader units 15. In falling downwardly over the chute in contact with or near the refractory bricks 20, the coal particles or lumps are subjected to drying efiects by the radiation they receive from the furnace combustion space 3 and the heat they receive by contact or radiation from the radiantly heated refractory bricks 20.

The spreader unit plates 14 at the bottom of the ramp 13 arrest the downward progress of the coal. When the coal particles or lumps are acted upon by the currents of air from the orifices 30, they undergo rearward accelerations. During such accelerations the shelf 23 prevents the coal as a whole from falling.

The currents of air from the orifices 30 fan out to a certain extent laterally, while moreover adjacent coal particles or lumps on each spreader unit plate 14 tend to be blown apart. Coal lumps and particles are, therefore, distributed also to each side of each spreader unit at the rear thereof, so that a satisfactory fuel bed is formed on the grate which extends across the whole width thereof.

The air from the orifices 30 and those coal particles or lumps destined to fall by gravity on the fuel bed of the grate travel at least initially in the same general direction with the air sweeping past such lumps or particles. The lumps or particles are, therefore, scrubbed by the air so that ample oxygen for rapid ignition and combustion of such lumps is available.

Air most closely adjacent the upper surface of the spreader unit plate 14 tends to flow adjacent the convex upper surface of the rearward part 80 thereof so that before it leaves the spreader unit it has a downward component of motion. Other layers of air adjacent the spreader unit plate also tend to a greater or less extent to leave the spreader unit closer to the grate than .they would if the spreader plate were horizontal throughout.

The larger lumps of coal, inasmuch as they have a smaller ratio of surface area to weight, tend to be less greatly accelerated by the air from the orifices 30 and less sustained by the mass of gas rising generally up wardly from the fuel bed on the grate and consequently they tend to fall nearer the front of the grate. Larger lumps require a longer time for their combustion than smaller lumps or particles, and this longer time they receive because the upper run of the grate moves rearwardly. Other lumps or particles having a larger ratio of surface area to weight are more greatly accelerated by the air from the orifices and have a speed when they reach the end of the track which renders them not greatly affected by the change in the direction of air flow adjacent the rear part of the spreader unit plate, and more sustained by the upwardly rising gas mass in the combustion chamber, as a result of which they tend to fall in the fuel bed at points more remote from the spreader unit.

Fine particles are very quickly accelerated by the air currents from the orifices 30 and are carried thereby into the upwardly moving mass of gas. Some are carried upwardly in the combustion chamber, mostly burning out in suspension. A large portion, if not most, however, are affected by the downward deflection of the air flow adjacent the rear part 80 of the spreader unit plate so as to be directed into the combustion space in a rearward direction which has a downward component of motion sufiicient to carry them towards the fuel bed; thereby adherence of fuel particles tothe fuel bed, burning out thereon and removal of the resulting ash with the main part of the ash at the rear of the grate is promoted.

The use of a downwardly curved deflector means, therefore, reduces the number of particles in suspension in the combustion chamber and by consequence the loss of solid combustible material leaving the furnace in the gases.

The spreader units 15 supply overfire air in a manner very efficiently assisting or promoting combustion in the space above the fuel bed on the grate. Additional overfire that may be required is provided through suitable secondary air nozzles.

Fig. 4 illustrates a modification of the spreader unit shown in Figs. 1 to 3, in which the part of the spreader unit plate 14 subsequent to the shelf 23 is bent to two curves. Thus the horizontal shelf 23 leads tangentially into a part 81 which provides a cylindrically curved surface arranged with its concave side upwardly, having a radius of 6" and where the surface makes an angle of 33 or thereahouts to the horizontal leading to a part 82, which provides a cylindrically curved surface arranged with its convex side upwardly, having a radius of 1%" and subtending an angle of 60 at its center. With this construction, the major part of the coal is discharged from the spreader unit in directions having upward components of motion, as is appropriate where the coal has to be distributed over a relatively long fuel bed. Many particles, however, of the finer sizes follow, to the rear of the spreader plate part 82, air from the orifices which tends to hug the upper surface of the plate and are there fore discharged from the spreader unit with downward components of motion.

Fig. 5 illustrates a variation of the modified spreader unit described with reference to Fig. 4, in which the curved plate part 81 is replaced by a flat plate 81, inclined to the horizontal at an angle of 33 or thereabouts, and the curved plate 82 is replaced by a substantially flat downwardly inclined plate 82.

Spreader stokers having shelves having little if any upward inclination upon which to accelerate fuel by pneumatic means for subsequent deflection which will result in the discharge of fuel at upward inclinations to the horizontal are disclosed and claimed in my copending application with John M. Miller and William M. Urquhart, Serial No. 338,812, filed February 25, 1953.

Fig. 6 illustrates a further modification in which the spreader plate 14 consists of a part 83, adjacent the block 19, which is cylindrically curved upwardly and rearwardly until it attains a small angle to thehorizontal, followed by a part 84 which is cylindrically curved with its convex surface upward, the inclination of the convex surface being downward at the rearmost end thereof.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. Combustion apparatus comprising walls defining a furnace, a horizontally disposed shelf positioned along one wall of said furnace intermediate the height thereof, an upwardly inclined deflector merging with said shelf at a position spaced from said wall inwardly of said furnace and having a downwardly inclined end portion thereby partially releasing fuel projected across said shelf and deflector in a downward direction, means for continuously delivering solid fuel at a selected rate to said shelf, horizontally disposed means for discharging an elastic fluid jet across the upper surface of said shelf, and a moving grate positioned in the lower portion of said furnace to collect ash and solid material thereon, said grate adapted to move in a horizontal direction across said furnace from a position adjacent the fuel inlet generally along the axis of the jet whereby the length of the path of travel of fuel on the fuel bed through said furnace is in a substantially direct proportion to the particle size.

2. The combination defined in claim 1, wherein said shelf and deflector include a substantially fiat horizontal surface projecting into said furnace from said wall, an upwardly curved upper surfacemerging with the furnace end of said fiat surface, and a reversely curved upper surface merging with the furnace end of said upwardly curved surface and subtending an angle of about 60 degrees therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 

